Sphygmomanometer cuff



Sept. 24, 1929. STEWART SPHYGMOMANOMETER CUFF Filed Jan. 19. 1927 INVENTOR A ATTORN Y Patented Sept. 24, 1929 UNITED STATES PATENT OFFICE THOMAS M. STEWART, OF ROCHESTER, NEW YORK, ASSIGNOR TO TAYLOR INSTRU- MENT COMPANIES, OF ROCHESTER/NEW YORK, A QORPORATION OF NEW YORK SPHYGIVIOMANOMETER- CUFL'f Application filed January 19, 1927.

This invention relates to-apparatus for indicating and recording the pressure characteristics of the blood stream in the human body and more in particular to an improvement of apparatus of the type disclosed in the Patent No. 1,582,705.

The apparatus referred to includes a double pneumatic cuff consisting of two separate flexible pneumatic containers adapted to be 19 applied, by means of a common enclosing jacket, to a suitable part of the body, preferably the upper arm, one behind the other in the direction of the flow of blood in the artery. .15 According to the theory of operation, the upper cuff has the function to variably constrict the artery while the lower cuff has the function to transmit the pressure impulses of the blood stream controlled by the upper 0 cuff to a special mechanism for indicating,

registering or recording the characteristics thereof and according to the same theory a recording mechanism should produce a plain line so long as the pneumatic pressure in the 2? cuffs is above the systolic pressure of the blood, and an oscillating line while the decreasing pneumatic pressure has a value lying between the systolic and the diastolic pressure.

It has been found that the accuracy of an instrument of the type involved is greatly affected by certain characteristics of the instrument, particularly by the characteristics of the cuffs.

It is the general object of the invention to provide a cuff construction which contributes in its own way to the production of correct pressure indications or records.

For a full understanding of the invention and its practical significance, reference is made to the accompanying drawings in which Fig. 1 is a plan view of a cuff construction embodying the invention;

Fig. 2 is a cross-section thereof;

.45 Fig. 8 is a cross-sectional view showing a part of Fig. 2 on an enlarged scale; and

Fig. 4 is a record which may be considered as a typical record produced as the, result of this invention. While heretofore the two pneumatic cuffs Serial No. 162,139.

were separate and structurally independent of each other, I have found that a much better and clearer record may be produced by making the two cuffs part of an integral structure. In addition I have found that the result can be further improved by reducing the effective distance between the two cuffs to the greatest possible extent.

I-Iaving reference to Fig. 4, the record includes a smooth or plain portion 10 and a plurality of oscillations or wave portions which first increase up to a maximum and then again decrease. The point 11 at which the first break in the smooth portion 10 takes place, denotes the systolic pressure while the point 12 may be assumed to indicate the diastolic pressure.

The important point, so far as the present invention is concerned, is the distinctive appearance of the first oscillation. There is no mistake about that point. This is in contradistinction to records of the prior art in which a plurality of minute points preceded more conspicuous breaks and in which it was impossible to say with certainty where the first break took place.

Having now reference to Figs. 13, the cuffs 14 and 15 are integrally connected and in fact form part of a unitary cuff'construction of elastic material, preferably rubber. They are separated by a common partition 16 and have pneumatic connections 14 and 15 respectively. The walls of the cuffs are preferably as thin as possible with due consideration of the maximum pressure conditions in the practical application.

In order to avoid the necessity of reinforce ments at the unction of the two cuffs, I place into the fabric a thin strip 17 of preferably inelastic material. This strip is disposed on that face of the cuff construction which is in use in contact with the arm or other part of the body because the Wearing strain incident to the expansion toward the arm is greater on that side, the outer surface being backed by the usual sleeve or acket.

I have found by comparative tests that the record produced by two cuffs in immediate juxtaposition as part of an integral cuff con struction is muchclearer and more definite than a record produced by two separate cuffs irrespective of their relative position. I have found in addition that adouble-cuff construction of the form shown and described considerably improves the character of the record as compared with an ordinary doublecuff construction.

While I do not claim that the theory on which I proceeded is correct in every detail, I believe the facts to be as follows:

The upper lat cuff has as the sole purpose to constrict and close the artery while the lower cuff 15 is to transmit the impulses of the blood stream to the recording mechanism. When the cuffs have been inflated through the connections M and 15 to such an extent thatthe upper cuff has completely stopped the flow of blood toward the lower cuff, no impulses are received by the lower cuff, with the result that the pen marks a substantially smooth line, viz the line 10.

As soon as the pressure has decreased to the value at which the peak of the pulsation operates to squeeze a small splash of blood through the portion of the artery compressed by the upper cuff, this splash has a certain kinetic energy which acts upon the lower cuff and from the latter the energy impulse is transmitted to and recorded by the recording mechanism.

In the arrangement described, the soft and pneumatically responsive part of the lower cuff being as close to the compressive portion of the upper cuff as is practically possible, the arterial interspace through which the blood has to pass before it can be effective upon the lower cuff is reduced to a minimum and the energy dissipated on the intervening arterial walls is a minimum. The impulse effect upon the lower cufl is therefore a maximum.

In the initial form of integral cuff construction in which for mechanical considerations I reinforced the junction of the two cuffs by thickening the walls, these thickened portions apparently constituted waste space, for the reinforcement on the upper side of the junction did not effectively compress and the reinforcement on the lower side of the junction was not sufficiently sensitive to transmit the pneumatic impulses. The arterial interspaee through which the blood had to pass before it could act upon a pneumatically sensitive part of the lower cuff, was longer and the dissipation of kinetic energy greater than with the form described.

This drawback was infinitely greater in connection with separate cuffs.

While I believe the above explanation to be correct, the construction shown and described has proved to mark a material advantage in the particular field.

I claim:

1. In apparatus of the character described, a pneumatic container of flexible material having walls of substantially uniform thick- 2. In apparatus of the character described,

a pneumatic container of elastic material having walls of substantially uniform thickness, a partition dividing the container into two separate chambers, a fluid connection to each chamber and means for strengthening the walls of the two chambers, comprising a thin strip of substantially inelastic material co-extensive with the partition and overlying the partition and portions of the adjoining walls.

3. In apparatus of the character described, a pneumatic container of elastic material having walls of substantially uniform thickness, a partition dividing the container into two separate chambers, a fluid connection to each chamber, the partition having a thickness and a width substantially equal to the thickness of the walls and a strip of substantially inelastic material co-extensive with the partition and overlying the partition and portions of the adjoining walls, the said strip having a thickness such as not to materially increase the thickness of the walls.

4. In apparatus of the character described, a normally flat pneumatic container of elastic material, a partition dividing the container into two separate chambers, said partition having a width such as not to materially increase the combined widths of the two Walls of the container and a thickness substantially of the order of the thickness of the walls, and a fluid connection to each of the chambers.

5. In apparatus of the character described, a normally flat pneumatic container of elastic material, a partition dividing the container into two separate chambers, said partition having a width such as not to materially increase the combined widths of the two walls of the container and a thickness substantially of the order of the thickness of the walls, a strip of substantially inelastic material coextensive wit-h the partition and overlying the partition and portions of the adjoining walls, the said strip having a thickness such as not to materially increase the thickness of the walls, and a fluid connection to each of said chambers.

In testimony whereof I affix my signature.

THOMAS M. STEWART. 

